This invention relates to heat exchangers, and is more particularly directed to a class of improved heat exchangers designed to realize the maximum transfer of heat with a minimum of heat transfer surface area and pressure loss in the fluids flowing therein.
In order to attain maximum thermodynamic performance, shell and tube or plate-fin type heat exchangers often employ many passes of cross flow stages in order to approach pure thermodynamic temperature distribution. The arrangement of Bond and Yi et al described in U.S. Pat. No. 4,962,810 yields the benefits of many passes in a compact, low pressure-drop design. The patent discloses a multipass heat exchanger comprising an arrangement of a plurality of heat exchanger modules, each module having a plurality of passes for passage of a first heat exchange fluid and a plurality of tubes across such passes for passage of a second heat exchange fluid. The heat exchanger modules are disposed in side-by-side relation, with each successive module adjoining the previous module in a stepped relation, the second exchanger module being positioned relative to the first module so that the first heat exchanger fluid leaving the first pass of the first heat exchanger module enters directly the second pass of the second module, and so on, in a straight through fashion, for as many passes as desired. The result is a highly efficient multipass heat exchanger of minimum weight and pressure loss in the flow path on the shell side of the exchanger, comprised of multiple heat exchanger units, with no reversal of flow in each pass in each exchanger unit.
U.S. Pat. No. 4,501,320 to Lipets et al discloses a multiflow tubular air heater employing a two-pass heat exchange concept embodying a Z-type bypass conduit. Other illustrative prior art heat exchangers are disclosed in U.S. Pat. Nos. 2,002,763; 2,327,491; 2,487,626; 3,180,406; and 4,559,996.
It is accordingly an object of this invention to provide a shell and tube type heat exchanger with essentially cross flow that has a configuration that yields the uniform temperature difference advantages of a pure counterflow design.
Another object of this invention is to eliminate the additional ducting at 40, 42 and 44 in the system of above U.S. Pat. No. 4,962,810 in order to "close" the flow circuits of the end modules in that system.
Another object is to provide a configuration compatible with gas turbine designs that has simple headers desirable as a wraparound regenerator for a gas turbine engine or heat exchanger in conjunction with a turboexpander device.
Yet another object is the provision of a basic heat exchanger design that can be optimized to provide minimum pressure drop for the service required by eliminating bends between passes and eliminating all headers and manifolds except for the inlet and outlet.
A further object is the employment of curved tubes and plates or baffles that relieve thermal stresses and the use of a cylindrical or barrel shaped case for said tubes and baffles to minimize thermal stresses and efficiently contain high internal pressure, these parameters being of particular importance during rapid thermal, flow, and pressure transients.